A woman has taken to Instagram to call out people who skinny shame her naturally slim physique.

Ally Trout, 42, a fitness blogger from Georgia, has been extremely slim her whole life, but decided to overhaul her body as her 40th birthday approached after issues with IBS frequently left her feeling bloated.

Her diet during her thirties mainly consisted of junk food, so Ally started the Kayla Itsines Bikini Body Guide with her husband, Kory, despite never exercising properly before.

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Skinny: Ally Trout, 42, a fitness blogger from Georgia, has been slim her whole life (left aged 32) but says she is frequently the target of skinny shamers online (right aged 42)

Shamers: Ally revealed that she has been told to 'go eat McDonalds' but thinks this is the 'dumbest idea on the planet'

However, despite her healthy new approach, the mom-of-two has revealed that she is the frequently targeted by skinny shamers online.

And although she says she eats several meals throughout the day, is often told she needs to eat more.

Posting a before and after shot of herself online, Ally captioned it with: 'People with private accounts love to tell me I’m too skinny and go eat McDonalds. That’s literally the dumbest idea on the planet.'

She continued: 'So no, I’m not a doctor (although I did make an A in graduate-level Behavior Modification so I know how to train your dog to grab you a beer out of the fridge) but I know if you want to gain healthy weight, you need to work your muscles and eat a surplus of NUTRITIOUS foods. Not junk.'

While most people struggle to lose weight, Ally is the opposite and has to make a conscious effort to maintain her current weight of around 100 pounds.

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Gym bunny: Ally ignores negative comments online and says she has to eat 1,800 calories per day just to maintain her current weight but her IBS sometimes makes this difficult

Banishing the bloat: A advocate of the low FODMAP diet, Ally avoids foods that cause bloating such as legumes, some vegetables and fruits and all refined carbohydrates

Trial and error: Ally likes to chart her progress using before and after pictures, left posing with her husband Kory in their thirties, and right in their forties

Without exercise this amounts to 1,500 calories per day, but as she works out most days, burning up to 300 calories at a time, she says she needs to eat around 1,800 calories to not lose anymore weight from her lean frame.

However, digestive issues, IBS and a 'small stomach' have made this harder than usual for Ally, and she is now an advocate of the low FODMAP diet.

This healthy eating plan forbids certain foods that are believed to be harder to digest like legumes, some fruits and vegetables and processed, refined carbohydrates.

She is also gluten-free and dairy-free.

'It’s hard when you have a small stomach and IBS. But I try!' she shared on her Instagram page.

A fan of posting before and after pictures online, Ally says she now doesn't rely on the scales and uses these shots to chart her progress.

Mixing it up: A fan of yoga, Ally also used the Kayla Itsines Bikini Body Guide to get fit

Inner strength: The outspoken blogger doesn't pay haters any attention and says she is happy to 'eat healthy and gain slowly'

Commenting on the picture and responding to the claims that Ally is unhealthy, registered dietitian Kay Dickson wrote: 'I like your attitude and think you have the perfect mindset on balance when it comes to weight gain.

'As someone has always been “skinny” without trying, I totally understand how frustrating it can be when someone tells you that you need to eat more.'

She added: 'Keep doing you, eating to fuel YOUR body, and eff the haters. This goes the same for someone who has some weight to lose, you gotta do it for you, not because of someone else’s negative opinion.'

A recent convert to yoga, Ally practices her poses at home early in the morning at 4am, and is committed to continuing her fitness journey.

Her plan for 2018? 'I’m not bulking and would never eat sh*t. Eating sh*t for years is what gave me IBS,' she wrote on Instagram.

A diet low in FODMAPs ('a Low FODMAP Diet') is scientifically proven, and is now used internationally, as the most effective dietary therapy for Irritable Bowel Syndrome (IBS) and symptoms of an irritable bowel.

Such symptoms include excessive wind (flatus), abdominal pain, bloating and distension, nausea and changes in bowel habits (diarrhoea and/or constipation). A Low FODMAP Diet has also been proven, with solid scientific research, to reduce symptoms of fatigue, lethargy and poor concentration.

FODMAP is an acronym that stands for:

Fermentable – meaning they are broken down (fermented) by bacteria in the large bowel

Oligosaccharides – 'oligo' means 'few' and 'saccharide' means sugar. These molecules made up of individual sugars joined together in a chain

Disaccharides – 'di' means two. This is a double sugar molecule.

Monosaccharides – 'mono' means single. This is a single-sugar molecule.

And

Polyols – these are sugar alcohols (however don't lead to intoxication)